Electric brake for electric motors.



M. KALLMANN. ELECTRIC BRAKE FOR ELECTRIC MQ'IORS.

APPLIOAIION FILED APB.23, 1907.

05 r Patented Nov/7; 1911.

' I I Fig.2. V

throughout the several views.

UNITED STATES PATENT orrrcn.

MARTIN 'KAZLIIJIVXANN. 0F BERLIN, GERMANY.

ELECTRIC BRAKE FOR ELECTRIC MOTORS.

1,007,705, Specification of Letters Patent. fa fig gd Nmn 7, 1.

Application filed April 23, 1907.. Serial No. 369,790.

\Vhile the variation resistance Fig. 1 is intended for strengths ofcurrents of about 2 amperes, when the wire is heated until it is redhot, the variation-resistances shown in Fig. 2 serve as a rule forstronger currents, as 5 or several amperes are required To all alum-z it mag concerm Be it known that I, MARTIN KALLMANN, engineer, citizen ofGermany, residing at Kurfuerstendamm tO/tl, Berlin, Germany, haveinvented certain new and useful Improvements in Electric Brakes forElectric Motors; and I do hereby declare the following to be a. full,clear, and exact description of the invention, such as will enableothers skilled in the art to which it appertains to make and use thesame.

The hereinafter described devices of electric brakes for elect-romotorsby the dynamoefi'ect or the so-called short circuiting is based on theuse ofresistances with very high positive tempcrature-coetlicients, forinstance iron. Resistances of this kind, which have already beendescribed by applicant for testing, measuring and starting purposes, (inapplication No. 287,373, filed Nov. 14, .1905) are in the followingbriefly called variation resistances. The value of these resistancesincreases about ten -fold when raised from a cold state to atemeraturerepresented by a bright cherry red.

Figures 1 and 2 show samples of such variation-resistances; Fig. 3 showshow the current changes if the motor, as dynamo, works on avariation-resistance; Figs. -l to 10 show dilierent systems of switchingon and off such variation short-cireuiting brakes.

in Fig. 1, 2 represents iron spiralsor other conductors of a very highpositivetem1)erature-coetlieient, such as for instance tantalum,wolfram, osmium or the like, all of which are however surpassed by iron.This variation-resistance 2 is in the inside of a glass reservoir 1,which is preferably filled with hydrogen for drawing oii the heat. andfor preventing at the same time oxidation. The iron spirals are held bya support (3 and, as a rule, by means of glasspearls or other insulatingmedium 3; 4 and 5 show the junction contact, for instance an Edisonsocket.

Fig. 2 shows a form of construction slightly difl'erent. from the above,in which the iron or other wire 2 is woundsingly or in several layersaround columns 3 covered by an insulating material, for instance kaolin.The whole carried by a support 6 in a hydrogen atmosphere in the glass1; danger of getting damaged. The diagram 4: and show the feed-contacts.for measuring such a brake-resistance to be Similar numerals refer tosimilar parts switched ofi in steps is the same as that for starters, asalso here the brake current must of several parallel Wires, to thebright cherry-red. The construction may of course be dilierent.According, to the eight of the tension several cells of such resistancesare connected in series, of whichlreach one is suliicient for 50 up to100 volts. According to the strength of the current required for brakingthe motor a correspondingly great number of resistances'hs connected inparallel.v Electro'motors were braked electrically hitherto byconnectingthe "10t01' switche oli" from the net with a resistance, sothat the'motor as a dynamo-machine generates current, which current isthe stronger the smaller the resistance connected to its terminals is.This braking method, which is generally called short-circuit braking,acts the more intensively the more work is put on the motor. It istherefore for the first moment it an ordinary, for instance nickelineresistance is used, strongest, and as the resistance remains constantitrapidly decreases when the speed of the motor and the strength of thecurrent sinks. The effect of the brak. therefore depends in an aboutquadratic proportion on the speed of the motor to be braked. In order tobrake rapidly and reliably it is necessary that such aconstantresistance, when the speed of the motor decreases be switched ofi" bymeans 0 a controller in several steps, by hand or automatically, inrapid succession, until it is perfectly, short-circuited, andtheoretically this switching ott of a constant resistance in steps musttake place at apaee such that the current is kept during the brakingperiod nearly constant on the highest value admissible for the motor.The more rapidly this ean take place the more rapidly the motor will bestopped. But if the strength of current admissible for the motorswitching cit of resistance the motor is in in order to heat this ironresistance, made is exceeded in consequence of a too rapid be maintainedwithin narrow limits on the highest admissible current. All. theseditficulties are avoided if instead of the ordinary resistances theabove described variation-resistances are used.

"Fig. 3 shows the diagram of the intensity ogf the current. Thevariation-resistance wfihich, if necessary, is heated up to incandecence, has at the beginning in the .cold st te a. very small value, sothat the motor switchedon' to it must supply a considerableinitial shockof current (point a of the curve) as dynamo, This initial shock ofcurrent, which may be made to be different according to thevariation-resistances, is further weakened, if it is necessary for thesafety of the motor, by switching on a proportionately small ordinary orconstant resistance, for instance of nickeline before the .ironresistance, in order to keep the initial value of both resistancestogether at a suflicient height, and limit the current thereby. Thisprecaution is however frequently not necessary, as in consequence of theshort duration of the shock of the current, damagmg of the armature orthe like need not be feared. But this short shock of current a acts inconsequence of the sudden and pronounced heating efi'ect veryadvantageously on the shortening of the time necessary for braking. Acondition is however. that the variators are made of very thinconductors which are easily heated and cooled, as a rule, of iron wireof a very small heat-capacity and therefore small inertia. Filling theglass boxes with hydrogen of a sufficient pressure also acts veryfavorably in this respect on account of the great heat conductingcapacity of the hydrogen. The wires must become hot almostinstantaneously, and when the current sinks, cool down again atonce.This action may be further favored .by plunging the glass vessels into a'cooling fluid. The specific resistance rises on being heated from thecold up to the redhot sta e nearly tenfold. After the first.

shock of the current a the current sinks to the normal value b on whichit is to be kept as constant as possible almost during the wholebraking-time (for instance 1' second) about up to point 0 of the curve.Toward the end of the braking-period the current must finally sink asthe speed, and thereby the tension produced, has considerablydecreasedand the resistance has become cold and cannot be more reduced andreaches at the end at the stopping point ate? the zero value. Ifnecessary, for instance, in-the case of large motors and considerableaccelerating influences of the motor switched off from the net, adivision ofthe variation-resistance into 2 steps, (but rarely more thantwo,) may be requiredforshortening the brakingtime. In order toaccelerate the stopping the complete short'circuiting of the resistanceby uand or' automatically may take place. For most cases however theself variability of the Variation-resistance alone is sutlicient withoutany artificial manipulations. as shown in Fig. 3. where the ordinaterepresents the current. the abscissa the duration or number ofrevolutions. The working is therefore such that by the initial shock ofcurrent of the motor acting as a dynamo the va iation-resistance isquickly heated until it is redhot and then cools down at the rate of thesinking of the tension or of the speed. and its specific resistance isautomati ally reduced.

The ditlerent connections in Figs. t to show the use, for some cases, ofthe working of shuntand series-direct currentanotors.

They can also be used for compound and other motors for hoists andlifts. t-ramways, automobiles and similar vehicles, and in other mannerfor three-phase motors and the like.

In Fig. 4 the shunt-motim 7, whose magnetic field is represented by 8 isafter switching-oft the starting-resistance 11 by means of the 'crank12, and after the disconnection from the net. connected with. theseries-eonnected variation-resistances and a part of thestartirig-resistance 11, by means of the crank and the contacts 13 and14-. Fig. 5 also shows a hand-starter on the motor 7, whose shunt isrepresented by S, but the starting-resistance 11. is not used for thebraking, but the crank 19, after s\\-'itching oft the resistance and thenet, swit hes the. armature by means of the contacts I? and 14 on thebra ire-resistance 9, l0 and 15, oiwhieh t) and I0 arevariation-resistances and 15 an ordinary resistance for weakening theinitial current.

Fig. 6 shows an automatic starter in corn nection with variationresistances. The. motor 7, whose n'iagnetic field is represented by 8,is in the position of the crank 17 on contact. 26 and 16 connected tothe net with the intercalation of the variation-resistances 20 and 21,and the constant snpplementm-y resistance 19. The winding of thestartingrelay is in this position, as will be seen, connected through 23and 26 to the armature 7 of themotor. After the motor has been started,thearmature 22 of the relay is drawn up as the. tension of the armatureincreases, and makes contact at 23 and 24, whereby thestarting-resistance is short circnitc'd: On the. switching off crank 17breaks the net and the winding of the relay at 16 and .26 and theloose-running motor 7 is connected over contact 18 with the.brake-resistance 9 and 10, which is formed by variation-resistance,whileat the same time, in consequence of the interruption whichautomatically takes place at 23 and 24, the starting resistance 19, 20,21 is during .the braking likewise in circuit. This may as a rule bedone without reducing the braking-current too much, as the cold startingvariation-resistanee possesses only a small value.

In Fig. 7 thestarting resistance is again represented by it 20, 21 andalso the other marks are the same as in Fig. t'. By moving the switch 17from i to 18 the startingresistance 20, '21 together with supplementaryweakening 1'e istu11c0, is connected to the armature 7,.and is thus usedfor starting and braking purposes. Fig. 8 shows again this arrangementof automatic starters with the same marks, but the switching oil of aspecial brake-resistance 9, 1t) and 17 takeplace here in two steps, asin the position of the crank 17 on contact- 1b the wholehraking-resistance S). 10, 15 is connected to the armature 7 of themotor and it moved t'arther on to contact only the-'ariat'iou-resistance 10 serves for the braking, in order to increasethe effect.

Fig. 9 shows a reversing automatic starter. The armature 7 of the shuntmotor selected as a sample here is in the position of the hipolar switch32, 33 on the contactand '25 connected to .the net, with the startingresistance 19, 20. ll intercalated.v \Vith the increased tension therelay 25 is more strongly excited and finally short-circuits, by-n1eansof the arm 22 of its iron-core at 23, 2-1: the starting-resistance,whereupon the full speed of the motor is attained. The magnetic field Sis for instance by closing the cut-out 27 directly connected to the netand possesses a parallel resistance- 34 for weaken ing theextra-current. in order to brake, the Switch 32, 2 3 is more or lessrapidly moved upon the contacts 29, 30 in consequence of which thearmature 7 is switched oti' from the net. and its starting resistance1!), "20, it

which has eventually automatically inter-- calated itselt' again, isconnected on the brake-resistance 9 and 10, made for instance of iron.()n the further movement. of switch 32, 33 upon the contact pieces 30,31 the motor will be restarted in the opposite direction, as thearmature current is new conducted to it. in the reverse direction.

Fig. 10 finally shows the application of the invention to series-motors.'lhe armature 7 is by moving the switch 36, 47 on the contacts 37, 39connected in series with the magnetic Held 3, and by moving the switch41, 49 on the contact 43, 43 the series-motor is started by the abovedescribed hand starter, u an automatic starter, and finally the startingresistance. is switched off. By switching 41, 42 on contact 44 and- 46the motor is however switched olt' from the net and acts, as will be.seen, as a dynamo-machine on the variation starting resistance 19, 2021, which in this case scrvesas a brake variat on-resistance. "ilhseries-motors the magnetic ticld 8 must, as is well known,

moreover be reversed on switching the brake on, which is effected byputting the switch 56, 47-011 contact 38 and 40. Also with series-motorsthe systems of switching described in the previous tigures can at'oncehe used. There is still to he noted. that the.

time up to the heating of the variation resistan es. it' the same aresutliciently sensitire. is only a small fraction ofa second, the same asfor instance the lighting up of incandescent lamps on being switched onand the extinguishing ot' the same on being switched oil". which canhardly be followed with the eye. The variators perfectly follow thedecrease in the speed of the motor from the startto the stop. ifneccssarygin the case of an excessively great brake-current, the thinwires of the variation-resistancewill themselves act as automaticsafeties, as by their rapid heating they weaken at once the dangerouscurrent, and in extreme eases melt, olt' like fuse-blocks, only stillmore rapidly and reliably, and reopen the braking current. Particularlyeasy is the application of this new braking-system with motors whichpossess already variationresistances for the starting, as these canthen, at the same time, be fully or partly used for the braking, butalso in the case of all ordinary motors the use of thevariationresistancc-brake ott'ers no ditiiculties, for instance onthree-phase motors in connection with the reversal of the rotating fieldby switching over of thetield-windin '1 claim-- 1. The combination of a.motor circuit, a starting resistance therein, a second resistanceelectrically controlled by the armature current when the motor is actingas a generator, said resistance last mentioned varying continuously withthe armature current by reason of the heating etl'ect thereof,independent of other conditons, and controlling indirectly by suchheating etieet the speed of the armature.

2.;Thc combination of a motor circuit, a resistance therein controlledby the armature current when the motor is acting as a generator, saidresistance varying continuously with the armature currentby reason ofthe heating eti'ect thereof, independent of other conditions, andcontrolling indirectly, by such heating eli'ect, the speed of thearmature, and means for automatically throwing theresistance intocircuit upon cutting 01? the currcntfrom the motor.

3. The combination of a motor circuit, a 4

' with the armature current by reason of the heating effect: thereof,independent of other conditions, and controlling indirectly, by suchheating etl'ect, the speed of the armature, means for throwing theresistance into circuit upon cutting off the current from the motor, anda constant resistance in series with the resistance before mentioned.

4. The combination of a motor circuit, a -i switch therein, a constantresistance and a '-resistance having a high positivetemperatureco-efiicient connected with said circuit, a solenoid, arms carried bythe core of the solenoid, a contact device adjacent to one of I 1" thearms and having connection with the coil of the solenoid, with theresistances, and with the 1110201 circuit, a second contact de-' ricelocated in the motor circuit, such arms and contact devices beingarranged to short. circuit the aforesaid resistances upon the excitationof the solenoid, and a conductor for connectin; the resistances with oneof the contacts of the switch.

in testimony whereof lttiliX my signature in presence of two witnesses.

MARTIN KXLLMANN.

, Witnesses: V

HENRY llixsrlcu.

